Bacillus Insecticides are not Acutely Harmful to Corals and Sponges

Abstract

Bacillus thuringiensis is a Gram-positive bacterium that produces crystalline endotoxins and is widely considered an environmentally safe insecticide to control mosquitoes and a number of agriculture pests. Bacteria closely related to B. thuringiensis have recently been discovered in association with diseased sponges, which has raised concerns that Bacillus insecticides may be harmfulopical marine invertebrates. We exposed coral larvae and juvenile corals to the insecticides VectoBac® G (containing B. thuringiensis israelensis) and VectoLex® G (containing B. sphaericus). VectoBac G and VectoLex G had no effect on the survival and metamorphosis of Acropora millepora and A. tenuis larvae at very high concentrations (5000 μ gl-1). The juvenile corals of the same species were also unaffected after 4 sequential 48 h exposures to B. thuringiensis israelensis and B. sphaericus at different stages of development. Adult corals (A. millepora) and sponges (Ianthella basta) wereposed to a single 6 h pulse of 1000 μ gl-1 VectoBac G. Although B. thuringiensis israelensis as detected in the seawater using denaturing gradient gel electrophoresis, it was not detected in association with the corals or sponges. No evidence of coral or sponge disease was observed during the following 2 wk. These results indicate that insecticides containing endotoxin-producing Bacillus spp. are unlikely to be acutely pathogenic to corals and sponges. However, the effect on most tropical marine invertebrates remain untested and the risks of seed populations of alien Bacillus becoming established on reefs and horizontal transfer of toxin genes to native bacteria also need to be addressed. © 2009 Inter-Research.